1. Field of the Invention
This invention relates to a photo detecting device comprising a photo-electron generating body, which absorbs light and generates photo-electrons, and a transistor, across which an electric current flows in accordance with a quantity of the photo-electrons having been generated by the photo-electron generating body.
2. Description of the Related Art
As photo detecting devices for converting light into electric currents and thereby detecting the light, photodiodes have heretofore been used widely. There have also been widely used phototransistors for amplifying photo-electrons by use of transistors and detecting the amplified photo-electrons. (The phototransistors are proposed in, for example, Japanese Unexamined Patent Publication Nos. 6(1994)-104477, 6(1994)-260674, and 11(1999)-017208.) However, nowadays there is a strong demand for a photo detecting device having an enhanced sensitivity in use applications, such as photo detection in long-distance optical communication, and detection of weak light in biochemical fields.
In view of the above circumstances, a photomultiplier for amplifying the photo-electrons by use of a vacuum tube has been proposed. There has also been proposed an avalanche photodiode (APD) for amplifying the photo-electrons by use of an avalanche multiplying layer and detecting the amplified photo-electrons. (The APD is proposed in, for example, Japanese Unexamined Patent Publication No. 5(1993)-029647.) It has been reported that the photomultiplier and the APD have large effects of amplifying the photo-electrons and yield larger photo-currents than with the conventional photodiodes and the conventional phototransistors.
However, with the photomultiplier, wherein the vacuum tube is utilized, the problems are encountered in that the stability with the passage of time is not capable of being kept good, and in that a sufficient quantum efficiency is not always capable of being kept. Also, in the fields of image sensors, biochemical analyses, and the like, it is desired that the photo detecting device is capable of being formed so as to have a two-dimensional array structure, and independent detecting operations are capable of being performed with respect to incident light impinging upon different sites. However, with the photomultiplier utilizing the vacuum tube, marked limitation is imposed upon the shape of the photomultiplier, and therefore the photomultiplier is not always capable of coping with the formation of the two-dimensional array structure.
The APD is capable of coping with the formation of the two-dimensional array structure. However, with the APD, the problems are encountered in that a signal-to-noise ratio is not capable of being kept high due to large dark current, and in that an accuracy, with which weak light is detected, is limited to a certain level. Accordingly, there is a strong demand for a photo detecting device having an enhanced sensitivity.